1. Field of Invention
This invention relates to lasers. Specifically, the present invention relates to systems and methods for detecting and correcting beam misalignment in systems employing multiple laser beams, such as projection display and other laser systems.
2. Description of the Related Art
Multiple laser beams are employed in various demanding applications including front and rear projection devices in movie theaters, home theater systems, heads-up displays for automobiles and aircraft cockpits, and design workstations. Such applications often require precise coaxial alignment of multiple laser beams for maximum display quality. Typically, each beam of the multiple beams is at a different frequency.
Undesirable laser beam deviation is particularly problematic in projection display applications, where beam misalignment may significantly degrade image quality. In laser projection systems, optical components may shift over time, creating corresponding undesirable laser beam path deviations, which degrade display quality. Consumers demand reliable high-quality displays.
An exemplary projection display system includes multiple coaxial laser beams, including red, blue, and green laser beams. A controller employs image information to generate control signals, which are provided to one or more light modulators and a scanner. The light modulators selectively modulate the intensity of each beam to adjust the overall color of the multiple coaxial beams in accordance with control signals received from the controller. A scanner (projection optics) then projects the modulated beams onto a screen, forming a dot (pixel) at a predetermined screen location. By scanning the entire screen and selectively controlling the color of each pixel via the light modulators and associated control signals, desired image information is displayed.
Misalignment of the coaxial beams relative to the desired optical axis degrades beam convergence on the screen, which degrades image quality. Furthermore, beam misalignment may prevent proper illumination of light modulator input surfaces, resulting in reduced display brightness, image artifacts, and preventing accurate non-uniformity correction, which results in undesirable pixel-to-pixel variations in screen intensity.
Laser applications employing multiple beams are relatively new, and beam orientation systems for automatically aligning plural laser beams have been slow to develop. Systems and methods for aligning an individual laser beam to a predetermined optical axis are known in the art. Unfortunately, existing systems generally cannot accurately and automatically detect beam misaligmnent and realign multiple laser beams or sets of closely spaced parallel beams.
Hence, a need exists in the art for an efficient system and method for automatically detecting and correcting laser beam misalignment. There exists a further need for a system that can efficiently and automatically detect and correct misalignment of plural beams directed along predetermined optical axis.
The need in the art is addressed by the system for detecting misalignment of plural beams of the present invention. In the illustrative embodiment, the inventive system is adapted for use with a laser projector. The system includes a first mechanism for automatically selectively isolating the individual component beams from the plural beams and providing each of the individual component beams as output in response thereto. A second mechanism detects misalignment relative to a desired optical axis of an individual component beam output from the first mechanism.
In a more specific embodiment, the system further includes a mechanism for automatically correcting the detected misalignment. The first mechanism includes a mechanism for sampling the plural beams and providing separated plural beams in response thereto. The mechanism for sampling includes a collimating lens or a pick-off beam splitter. The individual component beams include a red beam, a green beam, and a blue beam. A color wheel selectively isolates the red, green, and/or blue beams from the separated plural beams and provides an isolated component beam as output in response thereto. A beam splitter splits the isolated component beam into a first split beam and a second split beam and directs the first split beam and the second split beam along a first optical path and a second optical path, respectively. The first optical path terminates at a first detector, and the second optical path terminates at a second detector. The lengths of the first and second optical paths differ by a predetermined distance. A first control algorithm compares the relative position of the first split beam on the first detector to the position of the second split beam on the second detector with reference to the predetermined distance and provides a beam deviation signal in response thereto. A second control algorithm actuates a beam deviation correction system to correct the plural beams for beam deviations indicated by the beam deviation signal associated with the isolated beam.
In a first alternative embodiment, the first optical path passes through a first electrically controllable shutter, reflects from a first reflector, passes back through the beam splitter and then onto the surface of a single detector. The second optical path passes through a second electrically controllable shutter, reflects from a second reflector, passes back through the beam splitter and then onto the surface of the single detector. The second mechanism includes a computer for providing control signals to selectively shutter the first and second split beams via the first and second electrically controllable shutters to create first and second spots, respectively, on a surface of the single detector. The computer analyzes the positions of the first and second spots to measure beam deviation or misalignment associated with the isolated beam.
In a second alternative embodiment, the mechanism for redirecting a sample includes a first pick-off beam splitter in series with a second pick-off beam splitter for redirecting a first sample(s) of the plural beams along a first path and a second sample(s) of the plural beams along a second path, respectively. The first path passes through a first color wheel and terminates on the surface of a first detector. The second path passes through a second color wheel and terminates on the surface of a second detector. The first and second paths have predetermined differing lengths. A controller controls the first and second color wheels and calculates beam misalignment associated with isolated beams output from the first and second color wheels.
The novel design of the present invention is facilitated by the first mechanism, which allows individual component beams of plural laser beams to be automatically and selectively isolated and analyzed for beam position and orientation deviations from a desired optical axis. After component beam deviations are detected, they may then be corrected, resulting in precisely aligned plural beams. Consequently, by employing the plural beam deviation detection and correction systems of the present invention, accompanying laser projection systems and other applications requiring plural precisely aligned laser beams may operate more effectively and reliably.